In parts manufacturing using presses, there are two opposing ways to press a part. Traditional presses work much like a cookie-cutter, using a die to stamp the desired product from a larger solid piece of starting material. This type of press, though capable of quick repetition, necessitates large quantities of starting material—much of which simply goes unused in the stamping process—to produce the product. Furthermore, products manufactured by this type of press often require additional finishing work due to the inherent clumsiness of the mechanical stamping process, wear on the die, imperfections in the starting material, and various other problems.
More nimble than their traditional counterparts, hydraulic powder presses can inexpensively produce parts of great complexity without the scrap inherent in traditional stamping processes. Unlike traditional stamping presses, the hydraulic powder press uses a powdered starting material, which is placed into a die cavity and compressed between the walls of the die and one or more punches into the shape of the desired part. These presses customarily produce parts that exhibit a high quality and rarely require any additional finishing work.
Uniform material transfer is key to a powder press design that produces quality parts. Known simple gravity feed methods deliver particles into die cavities at a density that is roughly equivalent to the bulk density (i.e., density of a bulk volume of the particles) of the particulate material. Because of gravity and frictional forces, a die cavity does not fill uniformly under such circumstances and such feed systems do not provide a uniform density of particulate material within the die cavity. Articles produced by these feed methods are often unsatisfactory, as the compacted parts are of non-uniform density, which makes them more prone to stress related cracking, especially upon die cavity ejection. These cracks are often only visible after sintering.
A number of techniques have been developed in order to overcome the problem of non-uniform powder density in a powder press. One group of techniques is found in U.S. Pat. Nos. 5,885,625, 5,885,496 & 5,945,135. Each of these patents is directed to feed “shoes” and feed rings into which powder is disposed and fluidized using pulses of air in order to produce a uniformly dense powder. These devices are effective at eliminating the problem of disposing a uniformly dense powder within the die. However, the time required to fill these feed shoes and rings, close the necessary valves, fluidize the powder, and dispose the powder within the die cavity, is a significant limitation on the part-making capacity of a powder press.
Still another method, which was noted in the above-referenced patents, is commonly referred to as “shaking and baking.” Using this method, a feed shoe is attached to a stepper motor and filled with powder. Once the feed shoe is filled and placed over the ingress opening of the die cavity, the stepper motor causes the feed shoe quickly to move forward parallel to the ingress opening, stop, move back in the same parallel direction, and stop, in a manner similar to that used by bakers to encourage movement of flour through a sifter. Although this method is used to enhance movement of the powder, as noted in the above-referenced patents, it is ineffective at creating a powder with substantially uniform density.
Rapid uniform material transfer is key to a powder press design that produces quality parts quickly. Technologies exist for controlling and moving the mechanical parts of powder presses at much faster rates than those presently being employed. However, the rate at which powder presses can produce articles is limited by the rate at which the feed shoe, feed ring or die cavity can be filled with powder. This rate is relatively slow using gravity to feed powders into the feed shoe, feed ring or die cavity. Accordingly, the present invention increases the rate at which powder is delivered to a feed shoe, feed ring or die cavity of a powder press while still disposing a uniformly dense powder therethrough.